It is known to use differential scanning calorimeters (DSC) and thermal gravimetric analysis (TGA) machines to conduct thermal analyses of selected samples in order to examine certain characteristics of the samples as a function of temperature. Sometimes it is necessary to carry out measurements on a large number of samples; therefore, it is desirable and known in the art to mechanize the manipulation of the specimens, which is commonly referred to as autosampling.
One autosampler is shown in U.S. Pat No. 5,398,556 to Lang. Lang discloses a device comprising a vertical gripper member and a rotatable specimen plate for holding a plurality of specimen containers. The specimen container is transferred to the measuring location in the parent machine (such as the DSC or TGA) by rotating the specimen plate so that the desired specimen container is positioned under the gripper. Then, the gripper, which is driven by a motor, is lowered and gripping fingers attached to a gripping member grip the specimen container. The container is then raised from the specimen plate by raising the gripping member. The specimen plated is then rotated until a recess in the specimen plate is located underneath the gripping member. Next, the gripping member is lowered through the recess in the specimen plate and places the specimen container at the measuring location, which is directly underneath the gripper. The specimen container is then deposited on the measuring location by releasing the gripper fingers.
The gripper taught by the Lang patent is driven by two different drive motors and a cam mechanism; it is particularly disadvantageous in that the gripping motion itself is driven by a motor. As such, the gripper device taught by the Lang '556 is rather complicated in that it has many moving parts and if the motor over- or under-drives the gripper, then an error could occur in the placement of the sample. The device is further undesirable because the sample tray table rotates. A user must wait until the end of the sample run before the sample tray table can be removed and reloaded with additional samples.
What is desired, therefore, is an autosampler which does not require many moving parts, has a gripper wherein the gripping action is not driven by a motor, has a fixed sample tray table and which has a sample tray table that may be at least partially reloaded while the parent machine is conducting an analysis of selected samples.